Modular atomic force microscope with environmental controls

ABSTRACT

A modular Atomic Force Microscope that allows ultra-high resolution imaging and measurements in a wide variety of environmental conditions is described. The instrument permits such imaging and measurements in environments ranging from ambient to liquid or gas or extremely high or extremely low temperatures.

CROSS-REFERENCE OF RELATED APPLICATION

This application is a continuation application of U.S. Ser. No.14/817,517, filed Aug. 4, 2015, which was a continuation of Ser. No.13/998,691 filed Nov. 25, 2013, now U.S. Pat. No. 9,097,737 issued Aug.4, 2015 and entitled “Modular Atomic Force Microscope with EnvironmentalControls”, the disclosures of these parent applications are herebyincorporated by reference, in their entirety.

BACKGROUND OF THE INVENTION

Scanning probe devices such as the scanning Probe microscope (“SPM”) oratomic force microscope (“AFM”) can be used to obtain an image or otherinformation indicative of the features of a wide range of materials withmolecular and even atomic level resolution. In addition, AFMs and SPMsare capable of measuring forces accurately at the piconewton tomicronewton range, in a measurement mode known as a force-distance curveor force curve. As the demand for resolution has increased, requiringthe measurement of decreasingly smaller forces free of noise artifacts,the old generations of these devices are made obsolete. A demand forfaster results, requiring decreasingly smaller cantilevers, onlyreinforces this obsolescence. The preferable approach is a new devicethat addresses the central issue of measuring small forces with minimalnoise, while providing an array of modules optimizing the performance ofthe device when using small cantilevers or when doing specializedapplications such as optical techniques for biology, nanoindentation andelectrochemistry.

For the sake of convenience, the current description focuses on systemsand techniques that may be realized in particular embodiments ofscanning probe devices, the SPM or the AFM. Scanning probe devices alsoinclude such instruments as 3D molecular force probe instruments,scanning tunneling microscopes (“STMs”), high-resolution profilometers(including mechanical stylus profilometers), surface modificationinstruments, nanoindenters, chemical/biological sensing probes,instruments for electrical measurements and micro-actuated devices. Thesystems and techniques described herein may be realized in such otherscanning probe devices.

A SPM or AFM is a device which obtains topographical information (and/orother sample characteristics) while scanning (e.g., rastering) a sharptip on the end of a probe relative to the surface of the sample. Theinformation and characteristics are obtained by detecting changes in thedeflection or oscillation of the probe (e.g., by detecting small changesin amplitude, deflection, phase, frequency, etc., and using feedback toreturn the system to a reference state). By scanning the tip relative tothe sample, a map of the sample topography or other characteristics maybe obtained.

Changes in the deflection or oscillation of the probe are typicallydetected by an optical lever arrangement whereby a light beam isdirected onto the side of the probe opposite the tip. The beam reflectedfrom the probe illuminates a position sensitive detector (“PSD”). As thedeflection or oscillation of the probe changes, the position of thereflected spot on the PSD also changes, causing a change in the outputfrom the PSD. Changes in the deflection or oscillation of the probe aretypically made to trigger a change in the vertical position of the baseof the probe relative to the sample (referred to herein as a change inthe Z position, where Z is generally orthogonal to the X/Y plane definedby the sample), in order to maintain the deflection or oscillation at aconstant pre-set value. It is this feedback that is typically used togenerate a SPM or AFM image.

SPMs or AFMs can be operated in a number of different samplecharacterization modes, including contact modes where the tip of theprobe is in constant contact with the sample surface, and AC modes wherethe tip makes no contact or only intermittent contact with the surface.

Actuators are commonly used in SPMs and AFMs, for example to raster theprobe or to change the position of the base of the probe relative to thesample surface. The purpose of actuators is to provide relative movementbetween different parts of the SPM or AFM; for example, between the tipof the probe and the sample. For different purposes and differentresults, it may be useful to actuate the sample or the tip or somecombination of both. Sensors are also commonly used in SPMs and AFMs.They are used to detect movement, position, or other attributes ofvarious components of the SPM or AFM, including movement created byactuators.

For the purposes of this specification, unless otherwise indicated, theterm “actuator” refers to a broad array of devices that convert inputsignals into physical motion, including piezo activated flexures, piezotubes, piezo stacks, blocks, bimorphs, unimorphs, linear motors,electrostrictive actuators, electrostatic motors, capacitive motors,voice coil actuators and magnetostrictive actuators, and the term“sensor” or “position sensor” refers to a device that converts aphysical quantity such as displacement, velocity or acceleration intoone or more signals such as an electrical signal, including opticaldeflection detectors (including those referred to above as a PSD andthose described in U.S. Pat. No. 6,612,160, Apparatus and Method forIsolating and Measuring Movement in Metrology Apparatus), capacitivesensors, inductive sensors (including eddy current sensors),differential transformers (such as those described in U.S. Pat. No.7,038,443 and continuations thereof, Linear Variable DifferentialTransformers for High Precision Position Measurements, U.S. Pat. No.8,269,485 and continuations thereof, Linear Variable DifferentialTransformer with Digital Electronics, and U.S. Pat. No. 8,502,525, andcontinuations thereof, Integrated Micro-Actuator and Linear VariableDifferential Transformers for High Precision Position Measurements,which are hereby incorporated by reference in their entirety), variablereluctance, optical interferometry, strain gages, piezo sensors,magnetostrictive and electrostrictive sensors.

Some current SPM/AFMs can take images up to 100 um², but are typicallyused in the 1-10 um² regime. Such images typically require from four toten minutes to acquire. Efforts are currently being made to move towardwhat is sometimes called “video rate” imaging. Typically those who usethis term include producing images at the rate of one per second all theway to true video rate at the rate of 30 per second. Video rate imagingwould enable imaging moving samples, imaging more ephemeral events andsimply completing imaging on a more timely basis. One important meansfor moving toward video rate imaging is to decrease the mass of theprobe, thereby achieving a higher resonant frequency and as well a lowerspring constant.

Conventional SPM/AFM probes are currently 50-450 μm in length withspring constants of 0.01-200 N/m and fundamental resonant frequencies(f_(R)) of 10-500 kHz. Physical laws put lower limits on the achievableresolution and scan speed of conventional probes, given acceptable noiselevels.

To get the best resolution measurements, one wants the tip of the probeto exert only a low force on the sample. In biology, for example, oneoften deals with samples that are so soft that forces above 10 pN canmodify or damage the sample. This also holds true for high resolutionmeasurements on hard samples such as inorganic crystals, since higherforces have the effect of pushing the tip into the sample, increasingthe interaction area and thus lowering the resolution. For a givendeflection of the probe, the force increases with the spring constant(k) of the probe. When operating in air in AC modes where the tip makesonly intermittent contact with the sample surface, spring constantsbelow 30 N/m are desirable. For general operation in fluid, very smallspring constants (less then about 1.0 N/m) are desirable.

To get measurements with higher scan speeds, one wants probes with ahigh f_(R). After passing over a sample feature, the probe response isabout 1/f_(R) seconds for contact modes and Q/f_(R) seconds for AC modes(where Q is the quality factor for the probe). This sets a fundamentallimit on scanning speed: raising the response time of the probe requiresa probe with a high f_(R) or, in the case of AC modes, a low Q.

A higher f_(R) also means lower noise operation. The thermal noise of aprobe involves fixed noise energy of order kT (where k is the Boltzmannconstant and T is the temperature in Kelvin) spread over a frequencyrange up to approximately the f_(R). Thus, the higher f_(R), the lowerthe noise per unit band width below f_(R).

Probes with a high resonant frequency and a low spring constant can beachieved by making them smaller and thinner. However, using currentSPMs/AFMs with probes significantly smaller than conventional onespresents difficulties. In general, optimal optical lever detectionrequires that the spot from the light beam directed onto the side of theprobe opposite the tip should substantially fill the area available inone dimension. Underfilling results in a loss of optical lever detectionefficiency because the reflected beam diverges more than necessary.Overfilling the lever means losing light and producing unwantedinterference fringes due to light reflected off the sample.

One ideal probe for video rate imaging would have a f_(R) in the 5-10MHz range and a force constant in the 1-40 N/m range. This impliesshrinking conventional probes by an order of magnitude, to approximately5-8 μm in length or width. Such a shrinking, taken together with therequirement that the spot substantially fill the probe, means that thespot on the probe also must be shrunk. The optical system producing thebeam incident on the probe should have a numerical aperture (NA)sufficient with the wavelength of the light from the light source toform a focused spot approximately 5-8 μm in diameter in at least onedirection.

The relatively large numerical aperture required to so shrink the spotresults in a shallow depth of focus. This can present problems with therefocusing necessary when replacing one probe with another or when usinga probe with more than one cantilever. In addition, the large openingangle of the incident beam used to achieve a high numerical aperture canrequire complex lens systems or an accumulation of lenses in closeproximity to the probe.

A SPM/AFM that takes advantage of these smaller, high f_(R), highbandwidth probes is described in U.S. Pat. No. 8,370,906, Modular AtomicForce Microscope. The Cypher AFM manufactured by the assignee of thatpatent, as well as any patent resulting from the current application,provides a portion of the results forthcoming from these cantileverswithout their actual employment. With this instrument lower noisemeasurements and increased imaging rates are possible without the use ofsmaller, high f_(R), high bandwidth cantilevers. The Cypher AFMroutinely images point lattice defects in crystal surfaces in liquidenvironments.

In many applications the old generations of SPM/AFMs required the probeand sample to be relatively isolated in a local, user-controlledenvironment. Where the user was seeking an understanding of sampleproperties in a particular environment, for example in a particularliquid or particular gas, the sample and the probe used to sense thesample both had to be isolated and maintained at the environment ofinterest. The same was true where the user was seeking an understandingof sample properties at a particular temperature. In either case theenvironment so created also had to facilitate a compliant connectionbetween the sample and the probe so that when the sample moved relativeto the probe, or vice versa, the motion was minimally distorted and theimage and measurements also minimally distorted.

The requirement that an understanding of sample properties in aparticular environment or at a particular temperature means that thesample and the probe both have to be isolated and maintained at theenvironment or temperature of interest is of even greater importancewhen the when the user is employing smaller, high f_(R), high bandwidthprobes or is using a SPM/AFM like that described in U.S. Pat. No.8,370,906, Modular Atomic Force Microscope, (which includes the CypherAFM manufactured by the assignee of that patent). In order to fullyachieve the resolution and imaging rates made possible by these probesand SPM/AFMs when a particular environment or particular temperature isimportant, isolation is even more critical than with old generations ofSPM/AFMs.

FIG. 1 shows a cross section of a prior art apparatus for sealing theprobe and sample. In this design an o-ring 4020 or other flexible sealseals the volume around the probe 1040 and between the cantilever holder4010 and the sample 1030 mounted on the scanner 4000. The compliantnature of the o-ring 4020 produces relatively undistorted motion betweena moving sample scanner and static cantilever holder; or between astatic sample scanner and a moving cantilever holder.

However several performance issues arise with the apparatus shown inFIG. 1 The most significant is the relatively small diameter of typicalsealing elastomeric o-rings (˜1 mm) severely constrains our ability todesign an apparatus that eliminates distortion in the scanning motion.These o-rings simply are not compliant enough. The FIG. 1 design isnotorious for distorting the scanning motion of relatively weak openloop tube scanners. However, even with stiffer scanners employingpiezoelectric stacks and closed loop sensors, the FIG. 1 design willcause scanning motion distortion as the load dependent elasticity of theo-ring deflects the mechanical structure between the sample and X/Ysensors (not shown) housed in the sample scanner 4000. This isespecially obvious when the user is acquiring a series of relativelysmall images (scan of <100 nm) separated by relatively large (>5 um)offsets. As the o-ring relaxes after an offset, the relaxing forceexerted by the o-ring 4020 on the mechanical structure between thesample and the sample scanner 4000 causes creep in the subsequentlyacquired image, the more so the less time is allowed between scans.

Given the interest in observing dynamic phenomena, the cell designshould incorporate ports that allow for liquid and/or gas perfusionthereby allowing the cell environment to be changed during imaging orother measurements. The port positioning is important for ensuringcomplete exchange of fluid during perfusion experiments. Additionally,the cell should be able to maintain moderate pressures (˜5 psig) therebyallowing gravity flow perfusion. Gravity forced perfusion is a simple,yet noise free method for flowing liquids during AFM measurements.

Temperature dependent effects in materials are of extreme importance. Asdevices begin to shrink further into the sub-100 nm range following thetrend predicted by Moore's law, the topic of thermal properties andtransport in such nanoscale devices becomes increasingly important. Inaddition, basic material science requires in depth understanding of thenanoscale thermodynamics of materials. Polymer crystallization forexample, determines in great extent the macroscopic mechanicalproperties of the material but is mediated by nanoscale effects.

Temperature control on nanoscale devices while they are being measuredis also of great importance. Temperature differences between themeasurement point and the thermometry can cause significant errors inthe quantification of, for example, various thermodynamic transitionsincluding the melting and glass transitions in polymers.

FIG. 2 shows a cross section of a prior art heater for maintaining theprobe and sample at or near a particular temperature. These heaters useda sample block 1000 made of a material with a high thermal conductivity,such as copper. A heating element 1010 was included within or attachedto the block 1000 as was a temperature measuring means 1020. Thetemperature measuring means 1020 was of course used to measure thetemperature of the sample block 1000 and might also be used in a controlcircuit (not shown). The sample 1030 was mounted to the top surface ofthe sample block 1000 and the sample block was in turn mounted on ascanner (not shown). The probe 1040 was positioned above the sample.

One important challenge posed by the FIG. 2 heater is that thetemperature measuring means 1020 is extremely difficult to place next tothe region of the sample 1045 that is being imaged or measured by thetip of the probe 1040. Temperature gradients tend to make thetemperature of this region 1045 different from the temperature measuredby the temperature measuring means 1020.

A second challenge is minimizing image drift. To this end, materialswith low thermal expansion must be used in the mechanical structurebetween the sample and X/Y sensors (not shown) housed in the samplescanner (not shown) on which the sample block 1000 is mounted.

A third challenge is managing the extraction of excess heat. In heatingapplications it is critical to maximize the thermal resistance betweenthe sample heater and the elements of the mechanical structure betweenthe sample and X/Y sensors (not shown) which may expand/contract withtemperature changes and lead to degraded imaging performance. At anextreme, if the temperature of the Z-axis actuator rises above its Curietemperature, it will lose its actuation ability and the microscope willbe rendered inoperable. This same problem affects other SPM/AFMs coveredby prior art and has been solved by inserting a liquid cooled metalblock between the piezoelectric actuator and the heat source.Sufficiently thin and flexible rubber hoses connect this block to amechanical pump which circulates cooling water. Sufficiently pliablehoses will minimize scan distortion but often the mechanical vibrationsof the pump and the pulsation of the fluid flow will introduceundesirable noise and deteriorate instrument performance. Fluid leakswhich damage the instrument are also not uncommon.

A similar problem arises in cooling applications where thermoelectricdevices are an attractive and compact method for cooling the sample.With these devices the minimum temperature reachable on the cold side ofthe device depends heavily on the efficiency of heat extraction from thehot side. Active methods of extracting heat from the hot side of thedevice include using pumped coolant. Although pumped coolant is anefficient method for heat extractions it complicates the design with theaddition of pumps and fluid routing in a very constrained space.Additionally, pumps can add an unacceptable amount of acoustic andvibration noise to the SPM/AFM measurements.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Cross sectional view showing sealed cells in prior art.

FIG. 2: Cross sectional view of probe and sample heating in prior art.

FIG. 3: Block diagram showing a sealed cell using a rolling diaphragm.

FIG. 4: Block diagram showing a sealed cell using a rolling diaphragmwith an integrated o-ring.

FIG. 5: Block diagram showing a sealed cell using a rolling diaphragmwith an extended clamp.

FIG. 6: Cross sectional view of a rendered model of a sealed cell, alongwith its constituent components: cantilever holder, cell body, andsample stage.

FIG. 7: Cross sectional view of cantilever holder of sealed cell.

FIG. 8: Cross sectional view of cell body of sealed cell.

FIG. 9: Cross sectional view of sample stage of sealed cell.

FIG. 10: A block diagram showing the dovetail mounting of sample stage.

FIG. 11: A block diagram showing the integration of the dovetail to thez-actuator and X/Y actuator.

FIG. 12: Block diagram showing a method of sample heating with a heatingblock above the sample.

FIG. 13: Block diagram showing a method of sample heating methodproviding for an optical lever.

FIG. 14A,B,C: A block diagram showing different versions of samplestages providing for operation at high and low temperatures.

FIG. 15: A block diagram showing the heat flow from high temperatureheating unit.

FIG. 16: A block diagram showing passive heat dissipation design.

FIG. 17: A block diagram showing heat flow from high temperature heatingunit using passive heat dissipation design.

FIG. 18: Photographs of paper flexures, which illustrate how thin sheetsof HOPG materials can be used to passively extract heat withoutdistorting scanning.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 shows a cross section of the apparatus for isolating the probeand sample of the present invention. In this design the probe 1040 andsample 1030 are sealed in a chamber defined by the cantilever holder4010, a rolling diaphragm fabricated from hot/cold and chemicallyresistant elastomers among other possibilities 4030 and the scanner4000. The rolling diaphragm 4030 of the present invention provides amaximum of about one centimeter of clearance, an order of magnitudegreater than the one millimeter of clearance provided by the typicalo-ring used in the prior art sealing apparatus of FIG. 1. Accordinglythe stiffness of the rolling diaphragm is much smaller and the scanner4000 and cantilever holder 4010 move freely relative to each otherduring imaging and measurements. The smaller stiffness means that theforces on the mechanical structure between the sample 1030 and X/Ysensors (not shown) housed in the scanner 4000 are greatly reduced andhence scan distortion also.

Rolling diaphragms can be made of a variety of hot/cold and chemicallyresistant elastomers such as fluoroelastomers (for example Viton) orperfluoroelastomers (for example Kalrez). It is also possible i) tomanufacture composite rolling diaphragms with a thin Teflon sheet bondedto a less chemically inert rubber sheet, or ii) to form fabricreinforced rolling diaphragms, where the fabric layer reinforces thechemically inert elastomer layer so that the diaphragm can withstandhigher pressures.

In addition to creating a robust seal for isolating the probe and samplewithout compromising scan performance, a rolling diaphragm canrelatively easily accommodate a range of sample thicknesses. Rollingdiaphragms have primarily been used to create seals in pistons becausethey can seal over a large range of positions. For example, a rollingdiaphragm with an outer diameter of 23 mm, an inner diameter of 18 mm,and a height of 15 mm has a full stroke length of 10 mm, meaning that itcan accommodate sample thicknesses up to 10 mm.

It should also be noted that the use of a rolling diaphragm keeps scanperformance independent of the magnitude of the clamping force requiredto create the seal. In FIG. 3, the clamps 4040 used to seal the rollingdiaphragm membrane against the scanner 4000 and cantilever holder 4010can be tightened as much as is necessary. However, for the designdepicted in FIG. 1, the more the o-ring 4020 is compressed between thesample 1030 (or scanner 4000) and cantilever holder 4010 the more thescan performance is compromised because of the larger forces on themechanical structure between the sample 1030 and X/Y sensors (not shown)housed in the scanner 4000. Therefore minimizing o-ring 4020 compressionin FIG. 1 is advantageous for scan performance but this performancecould lead to possible leaks if the required compression is notachieved.

FIG. 4 shows an alternate design of a sealed cell for isolating theprobe and sample using the rolling diaphragm. The scanner 4000 of thisdesign has a groove 4060 which will accommodate an oversized bead oro-ring 4050 that is molded into one edge of the rolling diaphragm 4030.During assembly of the sealed cell, the inner diameter of the rollingdiaphragm 4030 is stretched around the scanner 4000 until it pullsitself into the groove 4060. The cross section of the bead or o-ring4050 of the rolling diaphragm 4030 has an appropriately oversized crosssection (10-40%) to make a tight seal. This design of the sealed cellhas the advantage that the rolling diaphragm 4030 is much more easilyattached and removed from the scanner 4000 for exchange or cleaning.

FIG. 5 is another alternate design of a sealed cell for isolating theprobe and sample using the rolling diaphragm. This design includes anextended clamp 4045 that aids in constraining motion of the rollingdiaphragm. This is especially useful when the cell has an over-pressure.

FIG. 6 shows a detailed rendering of a cross section of an apparatus forisolating the probe and sample of the present invention 4070, whichincorporates the concepts of the apparatus shown in FIG. 3, togethersimilarly detailed renderings of the major components of this apparatus,the cantilever holder 4080, cell body 4090, and sample stage 4100. Theapparatus depicted is constructed with chemically inert materials, andfor the most part materials able to withstand high temperatures withoutundergoing more than minimal thermal expansion. For the most demandingapplications it is possible to construct the entire interior of the cellout of fused silica with a perfluoroelastomeric rolling diaphragm. Themodular design of FIG. 6 has the advantage of allowing users toconstruct cells with different features optimized for their particularexperiment.

FIG. 7 is an enlarged rendering of the cantilever holder identified asitem 4080 in FIG. 6. The principal components of the cantilever holderof FIG. 7 are a support structure 4081, preferably made from INVAR oranother material with a low coefficient of thermal expansion, and with ahollow cylindrical shape at the center to accommodate the windowprovided by the cantilever holder body 4083; a cantilever holder body4083, preferably made from fused silica, or another chemically inertmaterial with a low coefficient of thermal expansion, which has atransparent window at the center to allow optical detection of thecantilever 1040; an o-ring 4082 which forms the seal between the cellbody, identified as item 4090 in FIG. 6, and the cantilever holder 4080;an actuator 4087 clamped between the support structure 4081 and thecantilever holder body 4083 to oscillate the cantilever; and acantilever clip 4084 for clamping the cantilever 1040 in place,preferably made from PEEK, stainless steel or any other chemically inertmaterial, which is sealed with o-ring 4085. In addition the cantileverholder 4080 provides two ports 4086 that permit liquids or gasses to beintroduced into the chamber that is formed by the cantilever holder4080, cell body 4090, and sample stage 4100

FIG. 8 is an enlarged rendering of the cell body identified as item 4090in FIG. 6. The cell body is constructed of a rigid support 4091,preferably made from INVAR or another material with a low coefficient ofthermal expansion and with a hollow cylindrical shape at the center. Theinside of the hollow cylindrical shape is lined with a tube 4092preferably made from fused silica. The tube 4092 could also be made fromother materials, but fused silica has the advantage of being chemicallyinert and transparent, so that a window allowing the user to look intothe chamber isolating the probe and sample that is formed by the thecantilever holder 4080, cell body 4090, and sample stage 4100. Optionalelectrical feed-throughs 4093 or gas or liquid ports 4094 may also beuseful.

FIG. 9 is an enlarged rendering of the sample stage identified as item4100 in FIG. 6. The sample stage has a sample platter 4101, preferablymade from chemically inert, low coefficient materials such as fusedsilica, that is bordered by a rolling diaphragm 4030, as discussed abovein connection with FIG. 3. If the sample stage has integratedtemperature control, a flex cable 4102, or other electrical connectionis required. Lastly, an interface such as a dovetail 4103 allows theuser to interchange different sample stages.

The dovetail 4103 is an important part of the design because, amongother reasons, it allows one sample stage to be interchanged withanother. In particular it allows the sample stage to be loaded top downinto a receiving fixture mounted on the scanner 4000 as shown in FIG.11, where the dovetail 4103 is being locked into place by a screw 4105forming part of a receiving dovetail 4104. The receiving dovetail 4104is attached firmly to the top of the scanner 4000.

The screw 4105 allows the sample stage 4100, to be loaded top down and,depending on the orientation of the receiving dovetail 4104 and screw4105, locked into place from the front, back, or sides of the scanner4000. Again depending on access, it may be possible to substitute onefully assembled cell 4070 for isolating the probe and sample of thepresent invention with another such cell. This is important for samplesthat need to be placed in the cell 4070 in a glove box or othernon-ambient environment. In this case the cell 4070 will be fullyassembled in the non-ambient environment, with the sample on the samplestage 4100, and then attached to the scanner 4000.

Of more fundamental importance, as the screw 4105 is turned to lock thedovetail 4103 in place, the dovetail experiences a downward force matingit firmly against the receiving dovetail 4104. This creates a highstiffness contact that is important for higher speed scanning. A lowstiffness connection between the sample stage 4100 and scanner 4000 willcause unwanted resonances that will decrease the scanning bandwidth.

Similarly, maintaining a high stiffness connection between the receivingdovetail 4104 and the scanner 4000 is important for maximizing the scanbandwidth and minimizing scan distortion. FIG. 11 deconstructs thescanner 4000 of FIG. 10 to show a screw 4003 binding the receivingdovetail 4104 to the scanner 4000 and also the component X/Y scanner4001 and tubular Z-axis actuator 4002 within the scanner 4000 (notpreviously shown). Tightening the screw 4003 compresses and preloads theactuator, making a high stiffness connection between the receivingdovetail 4104 and the scanner 4000.

In this embodiment of the present invention motion along the z-axishappens because the force generated by the z-actuator 4002 is able todeform the screw 4003 or thread interface between the screw 4003 and X/Yscanner 4001. A tubular stack piezoelectric actuator that is 10 mm talland has an inner and outer radius of 10/14 mm can generate a force of1400 N. Depending on the dimensions and threading of the screw 4003 thez-axis actuator loses little or no range, even when the screw is fullytightened.

In this embodiment of the present invention, the screw 4003 itself andthe thread interface between the X/Y scanner 4001 and the screw becomesa flexure. It is an extremely simple and inexpensive design and allowsfor easy assembly. More importantly however, it provides a method forpreloading the Z-axis actuator without introducing a flexure that mightallow rocking in the plane of the sample 1030. In this design thestiffness of the Z-axis actuator itself prevents the sample stage 4100and hence the sample 1030 from rocking. This design also provides for ahigh stiffness connection between the sample stage 4100 and the X/Yscanner 4001. Stiffness in the X/Y plane is important for a variety ofreasons, one of which is to avoid the application of small forces to thesample stage 4100 from the rolling diaphragm 4030 which would cause scandistortion. This embodiment minimizes those distortions because thestiffness of the Z-axis actuator itself prevents the receiving dovetail4104 from rocking or moving in the X/Y plane.

As already noted, in addition to sealing the probe and sample in orderto understand sample properties in a particular environment, similarisolation is necessary to maintain a temperature of interest where theuser was seeking an understanding of sample properties at a particulartemperature.

The prior art apparatus shown in FIG. 2 has the disadvantage thattemperature gradients tend to make the temperature of the region of thesample being measured different from the temperature measured bytemperature measuring means.

To avoid errors associated with temperature gradients, a plurality ofheaters can be used, geometrically positioned to minimize temperaturegradients in the sample region being probed. FIG. 12 shows such anapparatus. A heating element 1010 is included within or attached to thesample block 1000 as is a temperature measuring means 1020. Thetemperature measuring means 1020 is of course used to measure thetemperature of the sample block 1000 and might also be used in a controlcircuit (not shown). The sample 1030 is mounted to the top surface ofthe sample block 1000 and the sample block is in turn mounted on ascanner (not shown). The probe 1040 is positioned above the sample andinteracts with the sample. In addition a second block 1050, containing asecond heater 1060 and a second temperature measuring means 1070 (whichalso might be used in a control circuit (not shown)), is positionedabove the sample block 1000. By controlling the temperature of thesecond block 1050, it is possible to minimize the errors associated withtemperature gradients at the region 1045 of the sample being measured bythe probe 1040.

One important challenge posed by the apparatus of FIG. 12 is that thesecond block 1050 positioned above the sample block 1000 and the probe1040 may interfere with the functioning of other components of theSPM/AFM. In particular having a block positioned above the probe 1040may interfere with the optical lever arrangement whereby the amplitude,deflection, phase, frequency, etc. of the probe are detected bydirecting a light beam from above onto the side of the probe oppositethe tip.

FIG. 13 alters the FIG. 12 apparatus to correct the challenge notedabove. In the FIG. 13 apparatus a window 1100 is provided in the topblock 1050 to allow the transmission of light through the block. Thewindow 1100 allows an incoming (outgoing) beam 1080 and an outgoing(incoming) beam 1090 to be reflected off the back of the probe 1040 andto be used to measure the response of the tip as it interacts with thesample 1030. In one embodiment, the window is constructed of glass. Inanother, the window is a simple hole. In another, the entire top block1050 is constructed of an optically transparent material so that theincoming (outgoing) beam 1080 and an outgoing (incoming) beam 1090 canbe transmitted through an appropriate region of the block 1050.

Using a plurality of heaters to avoid errors associated with temperaturegradients provides another advantage when a window 1100 in the top block1050 of the FIG. 13 apparatus is used to avoid interfering with theoptical lever arrangement. With this arrangement condensation on thevarious components show in FIG. 13 is minimized or eliminated. This canbe especially useful for maintaining the window 1100 in the top block1050 clear and able to transmit light.

An apparatus 4070 for isolating the probe and sample of the presentinvention may be modified to operate at high and low temperatures. The4070 apparatus is depicted in cross sectional view in FIG. 6, togetherwith its major components, the cantilever holder 4080, cell body 4090,and sample stage 4100. For the purposes of discussing the modificationsnecessary for operation at high and low temperatures it will beconvenient to consult both FIG. 6, and particularly the sample stage4100, and FIG. 11, which as already noted is a cross sectional linedrawing of the sample stage 4100, together with the deconstructedscanner 4000 on which the sample stage 4100 is mounted.

FIG. 14A shows the modifications of the present invention to the samplestage 4100 necessary for operation at high temperatures, as high as1,000° C. The bottommost component 5000 of FIG. 14A corresponds to thedovetail, 4103 of FIG. 11 (which is also part 4103 of FIG. 9). Thedovetail allows the sample stage 4100 to be loaded top down into areceiving fixture mounted on the scanner 4000 as shown in FIG. 11, wherethe dovetail 4103 is being locked into place by a screw 4105 formingpart of a receiving dovetail 4104 mounted on the scanner 4000. In thecase of dovetail 5000 it is preferable to use a material that has a lowmass density, high mechanical strength, high stiffness, low coefficientof thermal expansion, and low coefficient of thermal conductivity. Onesuch material is Invar.

Dovetail 5000 supports a cylinder 5020 of smaller diameter made of rigidmaterial with a low coefficient of thermal expansion, a low coefficientof thermal conductivity and a high tolerance for high temperatures,preferably greater than 1,000° C. One such material is fused silica.Cylinder 5020 mechanically supports a heating element 5030, which alsomay serve as a sample support, preferably made of a material with a highcoefficient of thermal conductivity, a low coefficient of thermalexpansion and a high tolerance for high temperatures, preferably greaterthan 1,000° C. Diamond, silicon carbide, alumina or aluminum Nitride arepreferred materials, or a more elaborate embodiment—patterning aresistive metal trace onto the bottom of a heating element made of atemperature tolerant material—may be preferable. It may be desirable toattach a temperature sensor, preferably a platinum resistancethermometer (not shown) to the heating element 5030. Finally hightemperature tolerant wires (not shown) connect the heating element 5030and temperature sensors (not shown), via a hole in the dovetail 5000(not shown), to instrumentation electronics (not shown).

The dovetail 5000 also supports a second cylindrical structure 5010positioned outside cylinder 5020 which in turn connects to the rollingdiaphragm 4030. Since the typical elastomer material of which thediaphragm is made melts well below the maximum temperature of theheating element 5030, the cylindrical structure 5010 must be made of alow thermal conductivity material to thermally isolate the rollingdiaphragm 4030. Preferably the cylindrical structure 5010 is made offused silica or other low mass, low coefficient of thermal conductivitymaterial.

FIG. 14B shows the minor modifications to the sample stage 4100necessary for operation at ambient temperature. Again the bottommostcomponent 5040 of FIG. 14B corresponds to the dovetail, 4103 of FIG. 11(which is also part 4103 of FIG. 9). In this case, the dovetail 5040 ispreferably made of a material that has a low mass density, highmechanical strength, high stiffness, and low coefficient of thermalexpansion. One possible choice is Invar. The thermal conductivity of thematerial is of lesser importance.

The plate 5050 which serves as a sample support is separate from thedovetail 5040. This allows for embedded magnets between the two parts,which is useful for holding samples in a preferred position on theplate. The plate 5050 preferably has low coefficient of thermalexpansion, good mechanical strength and stiffness and a high degree ofchemical inertness. One possible choice is fused silica.

FIG. 14C shows the modifications of the present invention to the samplestage 4100 necessary for operating either below or above roomtemperature by means of a thermoelectric cooling element 5080. Such anelement can move heat from one place to another through the action of anelectrical current. This is known as the Peltier effect, and isreversible depending on the current direction though the TEC element5080. The TEC element is a useful means for cooling or heating a sample5080 with a single device.

As shown in FIG. 14C the TEC element 5080 is supported by dovetail 5060,which is preferably made of a material with a low coefficient of thermalexpansion, a high coefficient of thermal conductivity, a low massdensity and good mechanical strength and stiffness. Preferred materialsare diamond, aluminum nitride, silicon carbide and copper. The highcoefficient of thermal conductivity is particularly directed tooperation of the TEC element 5080 in cooling mode. In this case asignificant amount of waste heat is produced at the bottom of the TECelement 5080 and the dovetail 5060 must conduct this heat away to keepthe TEC element 5080 cool.

The TEC element 5080 directly supports a sample support 5070 whichsupports a sample (not shown). The sample support 5070 is preferablymade of material with a low coefficient of thermal expansion, a highcoefficient of thermal conductivity, good high mechanical strength andstiffness and good chemical resistance. Preferred materials are siliconcarbide, alumina, aluminum nitride, diamond, silicon, fused silica andstainless steel. It may also useful to attach or embed a temperaturesensor (not shown) in the sample support 5070. The temperature sensorwould be used for temperature feedback control of part 5070 and thesample that it supports. The rolling diaphragm 4030 may be attacheddirectly to part 5070 since the typical TEC element cannot operate abovethe limit where the rolling diaphragm 4030 will melt.

When electrical energy is converted to heat, that heat causes the localtemperature to rise and eventually the elevated temperature will causethe heat to flow to adjacent materials which are at a lower temperature.FIG. 15 depicts the flow of heat away from the high temperature heatingelement 5030 of FIG. 14A. Some heat arrow 5200 will flow into thesurrounding air. Since air conducts heat poorly, more heat will flowdown through the mechanical structure supporting the high temperatureheating element 5030. Arrow 5210 shows heat flowing from the hightemperature heating element 5030 to the dovetail 5000, which will causea rise in its temperature. Arrow 5300 shows heat flowing in turn fromthe dovetail 5000 to the receiving dovetail 4104 and then to to thetubular Z-axis actuator 4002 within the scanner 4000 (not shown) andfinally to the X/Y scanner 4001 also within the scanner 4000 (again notshown). All these components will rise in temperature as the heatcontinues to flow from the high temperature heating element 5030.

FIG. 16 shows the present invention's passive method for the extractionof unwanted heat flowing from the heating element 5030. This method isbased on the idea that heat which would otherwise flow on a path whichit is desirable to avoid can dissipated relatively harmlessly bypresenting the heat source with a second path with a much lower thermalresistance than the first path.

In FIG. 16 the dovetail 5000 is supported above the receiving dovetail4104 by three circular structures: a first ring 5105 sitting on thereceiving dovetail 4104 and preferably made from a material with a lowcoefficient of thermal conductivity, such as fused silica; a thinflexible second ring 5130 supported by the first ring 5105 which has ahigh coefficient of thermal conductivity, preferably higher than 400W/mK; and a third ring 5140 supported by the second ring and directlysupporting the dovetail 5000, which is made of a mechanically strong andrigid material with a high coefficient of thermal conductivity,preferably copper.

The outer perimeter of the thin flexible second ring 5130 ends withvapor filled heat pipe 5110 and the perimeter of the ring 5130 and theheat pipe 5110 are clamped between two copper annuli 5100 and 5120. Thecopper annuli 5100 and 5120 in turn are connected to a large thermallyconductive mass 5160, preferably made of aluminum or copper andpreferably cooled actively or passively by air or fluid flow, by meansof a vapor filled heat pipe or another means 5150 having a highcoefficient of thermal conductivity, preferably copper.

The flow of heat through the FIG. 16 construction is shown in FIG. 17.The arrows in FIG. 17 show the flow of heat away from heating element5030. As already noted, since air conducts heat poorly, only a smallportion of the heat will flow into the air above heating element 5030arrow 5200. Most of the heat will flow down through the low coefficientof thermal conductivity cylinder 5020 arrow 5210 and from there todovetail 5100. At this point, the heat flow splits into a path of highthermal resistance arrow 5250 and a path of low thermal resistance arrow5220. Most of the heat (arrow 5210 to arrow 5220 to arrow 5230 to arrow5240) will flow to part 5160, away from the critical components of theinstrument. Relatively little heat flows downward (arrow 5210 to arrow5250 to arrow 5260) into the critical parts of the SPM/AFM.

The thin flexible second ring 5130 supporting the dovetail 5000 has asnoted a high coefficient of thermal conductivity. Furthermore it ispreferably made of a material as flexible as the rolling diaphragm 4030described earlier. However, materials with a high coefficient of thermalconductivity (for example copper and diamond) are much more rigid thanthe materials used to make the rolling diaphragm 4030. Accordingly inorder to provide a material suitable for the thin flexible second ring5130 it was necessary to construct a proto-ring from thermallyconductive materials that are rigid, but can be formed into thinflexible sheets. FIG. 18 is a drawing of an arrangement of highlyordered pyrolytic graphite (commonly referred to as “HOPG”) stripsbridging an inner disc and an outer annulus. HOPG meets the preferredrequirement of a high coefficient of thermal conductivity. It has acoefficient of thermal conductivity greater than 300 W/mK. The innerdisc of an arrangement of HOPG strips like that shown in FIG. 18 caneasily tip, tilt, and move laterally in three dimensions. A stack ofmultiple thin strips of HOPG is preferred over a single layer of thickerstrips. In many cases, it is preferable to make these thin sheets lessthan 100 um, 75 um, or even as thin as 25 um or less.

In addition, it may be useful to layer the materials, interspersingmaterials with different thermal and mechanical properties. In oneembodiment, we have used a thin sheet of metal alloy that provides arelatively tough armor, protecting the thermally conductive materialfrom damage, either from manufacturing or normal use.

It is well known that the elastic properties of materials, in particularmaterials that are used to construct probes are temperature dependent.In addition, thermoelastic coupling, intrinsic damping due to defectmotion and generation cause non-trivial temperature dependent variationsin the dissipation and therefore Q-factor of the probe. This allcombines to make probe properties such as the spring constant andquality factor temperature dependent. Furthermore when we add theeffects of possible condensation from the sample or elements of the AFM,the properties of a probe may vary significantly as the temperaturechanges.

Given that the mechanical properties of the probe are temperaturedependent, there are a number of solutions that allow these changes tobe taken into account for the purposes of optimizing SPM/AFMmeasurements. In particular, the probe can be tuned between measurementsand the drive parameters adjusted to reflect changes in the response ofthe probe flowing from changes in temperature and other factors. If aparticular free-air amplitude and relationship to the probe resonancefrequency is required, the drive amplitude and frequency of the probeactuation can be adjusted after the tune is made to reset the probe.Other methods can be used to estimate the probe spring constant (see forexample J. E. Sader et al. Rev. of ScientificC Ins. 83, 103705 (2012)).This spring constant can then be used in conjunction with thermal noisemeasurements to yield the optical lever sensitivity of the probe andother properties that allow quantification of the measurements as in thecommercially available GetReal™ product offered by the assignee of thispatent.

Some users, U.S. Pat. Nos. 6,389,886 and 6,185,992, have taken thiscorrelation of temperature and probe mechanical properties relationshipto mean that temperature in one component of the AFM apparatus should beadjusted to maintain one or more of these properties at a preset value.This approach very likely guarantees that the probe is being driven, forexample, off resonance and in any event in a sub-optimal manner. Forexample, if the temperature changes in the SPM/AFM, the chip of theprobe or the cantilever holder may be distorted due to the expansion ofthe material from which they are fabricated. This distortion may be incompetition with the temperature dependence of the probe. If we take theapproach of adjusting the temperature of the top plate, the resultingbending of the probe will be non-zero, leading to errors.

These effects also imply that the cantilever will be immersed in asubstantial temperature gradient since in general, the two heatedcomponents of the SPM/AFM are at different temperatures. Temperaturegradients are undesirable for AFM measurements for a number of reasons.One is that the actual temperature of the sample surface is ill-defined.The approach we take is substantially different.

First, by substantially eliminating temperature gradients, we improvethe thermometry of the sample. We also measure the operating parametersof the SPM/AFM as a function of the mechanical properties of the probe.Then when there is a change in temperature we first allow the probe torespond to that change and after it has we adjust the operatingparameters to respond to the change so that the probe is still operatingat its natural resonant frequency or at a preset relationship near theresonant frequency. Putting it another way, we accept the fact thattemperature effects will change the behavior of the cantilever probe andit is therefore necessary to adjust the operating parameters of themicroscope to respond to what is in effect a “new” cantilever with newmechanical properties. If, as is taught in the prior art, one insteadchanges the temperature of the top plate to force a cantilever parameterback to some preset value, there can be many disadvantages. First and inmany cases foremost is the introduction of temperature gradients in thecell since there is usually a difference between the temperature of thetop plate and the bottom plate. As an ancillary effect, this can alsoresult in driving the cantilever off resonance since the resonantfrequency may change in response to the temperature and temperaturegradients required to keep the other parameter—the deflection—constant.

Although only a few embodiments have been disclosed in detail above,other embodiments are possible and the inventors intend these to beencompassed within this specification. The specification describesspecific examples to accomplish a more general goal that may beaccomplished in another way. This disclosure is intended to beexemplary, and the claims are intended to cover any modification oralternative which might be predictable to a person having ordinary skillin the art. For example, other devices, and forms of modularity, can beused.

Also, the inventors intend that only those claims which use the words“means for” are intended to be interpreted under 35 USC 112, sixthparagraph. Moreover, no limitations from the specification are intendedto be read into any claims, unless those limitations are expresslyincluded in the claims. The computers described herein may be any kindof computer, either general purpose, or some specific purpose computersuch as a workstation. The computer may be a Pentium class computer,running Windows XP or Linux, or may be a Macintosh computer. Thecomputer may also be a handheld computer, such as a PDA, cellphone, orlaptop.

The programs may be written in C, or Java, Brew or any other programminglanguage. The programs may be resident on a storage medium, e.g.,magnetic or optical, e.g. the computer hard drive, a removable disk ormedia such as a memory stick or SD media, or other removable medium. Theprograms may also be run over a network, for example, with a server orother machine sending signals to the local machine, which allows thelocal machine to carry out the operations described herein.

What is claimed is:
 1. An atomic force microscope system, comprising: anatomic force microscope cantilever, having a tip, said cantilever on acantilever holder; a sample block, having a top surface adapted for aholding a sample to be measured by the atomic force microscopecantilever; a rolling diaphragm, formed of a flexible membrane material,said rolling diaphragm sealing between said sample block and saidcantilever holder to form a sealed chamber between said sample block andsaid cantilever holder; a scanning mechanism, operable for moving thesample block while said rolling diaphragm maintaining said sealedchamber between said sample block and to said cantilever holder, whereinsaid rolling diaphragm allows at least 10 mm of movement between saidsample block and said cantilever holder while maintaining said sealedchamber between said sample block and said cantilever holder; where theatomic force microscope cantilever is above the sample block; saidsample block including a heater which heats the sample block, andincluding a temperature sensor that senses a temperature of the sampleblock; a second block, above the atomic force microscope cantilever, andabove the sample block; the second block having a second heater and asecond temperature sensor, a controller that controls temperatures ofthe sample block and the second block to avoid temperature gradients ina region of the sample.
 2. The system as in claim 1, further comprisinga detecting system that detects a position of the cantilever using anoptical lever directed on to the cantilever.
 3. The system as in claim2, wherein the second block includes a window therein, and the opticallever is directed through the window to the cantilever, and a reflectionfrom the cantilever is directed through the window.
 4. The system ofclaim 3, wherein the window is constructed of an optically transparentmaterial.
 5. The system as in claim 2, wherein the second block isformed of an optically transparent material, and the optical lever isdirected through the optically transparent material to the cantilever,and reflection from the cantilever is directed through the opticallytransparent material.
 6. The system as in claim 1, wherein the sampleblock and the second block are controlled to the same temperature. 7.The system as in claim 1, further comprising the sample, whosecharacteristics are monitored by the cantilever.
 8. A method ofoperating an atomic force microscope system, comprising: using an atomicforce microscope cantilever, having a tip to monitor characteristics ofa sample that is mounted on a top surface of a sample block; where theatomic force microscope cantilever is above the sample block; using arolling diaphragm, formed of a flexible membrane material, for sealingbetween said sample block and said cantilever holder to form a sealedchamber between said sample block and said cantilever holder; using ascanning mechanism for moving the sample block while said rollingdiaphragm maintaining said sample block sealed chamber between saidsample block and to said cantilever holder, wherein said rollingdiaphragm allows at least 10 mm of movement between said sample blockand said cantilever holder while maintaining said sealed chamber betweensaid sample block and said cantilever holder; using a heater for heatingsaid sample block; using a temperature sensor for sensing a temperatureof the sample block; locating a second block above the an atomic forcemicroscope cantilever, and above the sample block; using a second heaterfor heating the second block; using a second temperature sensor forsensing a second temperature of the second block; and controllingtemperatures of the sample block and the second block to avoidtemperature gradients in a region of the sample.
 9. The method as inclaim 8, further comprising detecting a position of the cantilever usingan optical lever directed on to the cantilever.
 10. The method as inclaim 9, wherein the second block includes a window therein, and furthercomprising directing a beam from the optical lever through the window tothe cantilever, and a reflection from the cantilever through the window.11. The method as in claim 10, wherein the window is constructed of anoptically transparent material.
 12. The method as in claim 9, whereinthe second block is formed of an optically transparent material, anddirecting the optical lever through the optically transparent materialto the cantilever, and directing a reflection from the cantileverthrough the optically transparent material.
 13. The method as in claim8, further comprising controlling the top plate and the bottom plate tothe same temperature.
 14. The method as in claim 8, further comprisingadjusting to a change in temperature by first allowing the cantilever torespond to a new temperature, and after the cantilever has adjusted tothe new temperature, adjusting operating parameters of the cantilever tooperate the cantilever at its natural resonant frequency for the newtemperature.
 15. The method as in claim 8, further comprising adjustingto a change in temperature by first allowing the cantilever to respondto a new temperature, and after the cantilever has adjusted to the newtemperature, adjusting operating parameters of the cantilever to operatethe cantilever at a preset relationship near a resonant frequency forthe new temperature.